Patent GB-756323-A (GB)
Title: Telephone systems including main and satellite exchanges
IPC: H04Q3/58
Filed: 1952-07-03
Abstract: 756,323. Automatic exchange systems. LICENTIA PATENT - VERWALTUNGS-GES. July 3, 1952 [July 3, 1951; Sept. 10, 1951], No. 16744/52. Class 40 (4). In a system in which an automatic satellite (non-exchange) is connected over a plurality of junctions to an exchange and receives all necessary current from the exchange, each junction has a set of control and switching circuits at each end and a fault occurring in a junction or its associated circuits automatically results in that junction being isolated and in calls being routed over other junctions. At the satellite each junction terminates in a relay switch which htmts for a calling line and is set to a called line and is similar to that described in Specification 732,354. The relay switches are controlled in a similar manner to that described in Specification 706,880, [Group XXXVIII]. At the exchange each junction branches, one branch terminating in a wiper switch which is stepped synchronously with the associated relay switch and which for an incoming call hunts for the marked final selector outlet and for an outgoing call busies the corresponding outlet of the final selector multiple, and the other branch terminates in a preselector. Relays A, B at the satellite and A, B, R at the exchange are normally operated. Outgoing call from satellite. Closure of the caller's loop earths the common start wire An to operate relays D, M associated with the allotted junction VL1. Relay A releases and momentraily disconnects earth from the wire a to send a starting signal to the exchange. Relay M falls back and connects earth by a low in place of a high resistance path to the wire b. At the exchange, the starting signal releases A, whereupon W seizes a preselector VW and connects an impulsing relay J to the wire a. Relay J interacts with the magnet of a switch AW and a relay switch RW at the satellite which steps synchronously with the switch AW in search of the calling subscriber's line. Relay R falls back and presents junction VL2 to the final selector multiple and disconnects junction VL1 therefrom. When the caller's line is reached opposed windings of B are energized and J is disconnected. Switch AW connects up the caller's meter. At the exchange a circuit is completed when the switch AW stops for relays C, K. Relay disconnects B and also battery from the wire b. The release of B and of a previously operated relay H switches the caller through to the preselector and relays F, T1 in the speech wires are energized to disconnect the controlling relays from the junction. Incoming call to satellite. When the final selector reaches the wanted outlet, a relay E associated with a free junction VL1 disconnects battery from the wire a, releases A and operates G. The last relay shunts down E to connect up the impulsing relay J. At the satellite, relay A falls back to connect up the relay selector RW and to disconnect the start wire An and when the selector RW moves from normal relay S1 connects low in place of high resistance earth to the wire b to operate a marginal relay T at the exchange which relay completes the test circuit for switch AW. The relay selector RW and switch AW step synchronously by interaction with relay J until the latter reaches the outlet marked by the selector LW whereupon test relay C disconnects J, T and battery from wires a, b. In the satellite, relays B, H fall back and ringing current is applied from the final selector LW. When the called party answers, relays F, T1 disconnect the controlling relays. Release. In the case of an outgoing call release by the called party causes W to fall back followed by C, K, which disconnect the line wires a, b so releasing relays F, T1. At the satellite a circuit is completed over wire b for M which releases selector RW and operates relays A, B before falling back. At the exchange, B is energized over wire b and brings up A to return switch AW to normal, whereupon R pulls up. In the case of an incoming call, the release of the final selector disconnects C and the circuits return to normal as described above. Fault. Should relay A at the exchange fail to release in response to the calling signal, the relay T is not short circuited so that when at the satellite low resistance earth is applied to the wire b, marginal relay T operates and connects up a thermal relay Th which after some delay operates an alarm relay AL. The alarm relay AL locks up and relays A, B, R release so disconnecting current from the line wires and preparing another junction VL2. All operated relays at the satellite release whereupon the start wire An is connected to junction VL2. An earth fault on the wire a releases A at the satellite and so connects the start wire to the next free junction. An earth fault on the wire b sufficient to shunt down relay B at the satellite is also sufficient to operate the marginal relay T with results as described above. In the case of an incoming call, should the apparatus at the satellite fail to respond, the marginal relay T is not operated. Thus, since V is operated while the switch AW hunts, the test circuit of AW is not closed and the switch rotates until the thermal relay Th operates AL, whereupon the junction VL1 is released. If the impulsing relay J fails to function, V remains up and operates Th. Preventing certain satellite subscribers making calls. A key SPT1 at the exchange is thrown to apply battery to an outlet in the bank d of switch AW so that an attempt to make a call by the corresponding subscriber results in the operation of the exchange relay K alone when the line loop is reached by the selector RW. Relay K shunts down B which removes the short circuit on T, which earths the wire b. Relays A, R release. At the satellite, relays H, D release and connect the caller to the junction, whereupon relays F, T1 operate. However, at the exchange the junction has not been connected to a preselector since relay C is unoperated. Thus dialling tone is not reverted. Should the subscriber attempt to dial, the first impulse releases W and so the junction. Alternatively, W may be slow releasing so that release of the junction is delayed until the caller hangs up. In a modification, the alarm relay when operated, earths wire b, locks to the wire d but has no other holding circuit. Thus in the case of an earth fault on the wire a or a permanent loop condition the alarm relay AL holds until the fault is removed but when say one of the junction wires is broken the alarm relay AL is operated intermittently; it being arranged that operation of the alarm relay causes de-energization of the thermal relay Th.